This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The goal of our research is to apply structural biology and high performance computer simulation to investigate molecular mechanisms of bacterial resistance to mercury. Specifically we are interested in solving the first ever X-ray crystal structure of the metal-responsive transcriptional regulator MerR. MerR is the archetype of the MerR family of metalloregulators that controls the transcription of a set of genes (the mer operon) providing Hg resistance in many genera of bacteria isolated from Hg-exposed ecosystems. The mer operon encodes specific genes that facilitate transport of Hg species cleavage of organomercurials and reduction of ionic Hg(II) to volatile elemental Hg(0). The 144-residue MerR binds to its operator DNA and functions as a homodimer. It represses transcription of the mer operon in the absence of Hg(II) and activates transcription upon Hg(II) binding. We wish to obtain a high resolution model to fully characterize Hg(II) binding to MerR. This structural model of MerR will support ongoing neutron scattering and Molecular Dynamics (MD) experiments aimed at studying MerR dynamics and conformational changes upon Hg(II) binding that are essential for understanding its unique mechanism of transcriptional regulation. It is well-known that these multidisciplinary structural studies require maximal resolution X-ray structures of the protein element. As a result a high flux beamline is required to collect high quality data for this proposed research. One day of beamtime (3 shifts) is requested to complete the proposed diffraction studies. We plan to screen crystals of MerR for X-ray diffraction quality and to collect complete redundant data at the highest resolution possible. Structure determination will then be completed by molecular replacement using either a known structure of a paralogous member of the MerR family or by using our current homology model of MerR.